Magnetizing apparatus and method

ABSTRACT

Apparatus and method for magnetizing a permanent magnet rotor member for a dynamoelectric machine, the rotor member including four members formed of permanent magnet material each having transversely spaced surface areas to be oppositely polarized. A magnetic stator core member is provided having a yoke portion with a plurality of radially inwardly extending teeth defining winding slots therebetween, the teeth being divided into four circumferentially spaced groups and having inner ends defining a bore for receiving the rotor member. Four windings are provided each comprising a plurality of concentric coils distributed in respective ones of the slots of one of the groups of teeth. The windings are connected in parallel and arranged when energized to excite alternate tooth groups to form opposite poles respectively aligned with the areas to be polarized. A capacitor discharge power supply is coupled to the windings for producing thereacross a momentary high voltage pulse of preselected magnitude thereby to cause a highly peaked surge of current flow in the windings. The preferred method includes establishing a short duration highly peaked magnetic field in preselected regions of space and magnetizing permanently magnetizable members previously disposed in those regions.

United States Patent [151 3,678,436 Herdrich et al. [451 July 18, 1972[54] MAGNETIZING APPARATUS AND [57] ABSTRACT THOD Apparatus and methodfor magnetizing a permanent magnet [72] Inventors: William M. Herdrich;Norman A. B nd rotor member for a dynamoelectric machine, the rotor bothof Fort Wayne, Ind. member including four members formed of permanentmagnet material each having transversely spaced surface areas to [73]Asslgnee' General Electric Company be oppositely polarized. A magneticstator core member is [22] Filed: May 24, 1971 provided having a yokeportion with a plurality of radially inwardly extending teeth definingwinding slots therebetween, [21] 6J3: the teeth being divided into fourcircumferentially spaced groups and having inner ends defining a borefor receiving the [52] US. Cl ..335/284, 310/156 rotor member. Fourwindings are provided each comprising a 1 /00 plurality of concentriccoils distributed in respective ones of [58] Field of Search ..335/284;310/156 the lot of one of the groups of teeth. The windings areconnected in parallel and arranged when energized to excite al- [56]References Cited temate tooth groups to form opposite poles respectivelyUNITED STATES PATENTS aligned with the areas to be polarized. Acapacitor discharge power supply [8 coupled to the WlIldll'lgS forproducing 2,439,827 4/1948 Sterenbuch et al. ..335/284 thereacross amomentary high voltage pulse of preselected 3,335,377 8/1967 Kohlhagen..'...335/284 magnitude thereby to cause a highly peaked surge ofcurrent Primary Examiner-George Harris Attorney-John M. Stoudt, Ralph E.Krisher, Jr., Radford M.

Reams, Joseph B. Forman, Frank L. Neuhauser and Oscar B. Waddel] 68 {bnun flow in the windings. The preferred method includes establishing ashort duration highly peaked magnetic field in preselected regions ofspace and magnetizing permanently magnetizable members previouslydisposed in those regions.

14 Claims, 5 Drawing Figures PNENTEU JUH 81972 SHEET 1 BF 2 D.C.SURGEPOWER SUPPLY //Vl E/\/7'0,?.S. WILLIAM M. HERDRICH NORMAN A. BENDER A TTORNE Y PATENIEDJULWW 3,6?8,436

sum 2 or 2 9s 90 52 78 so 38 32 92 9o 4 INTERLOCK [6 INVENTORS l IWILLIAM MHERDRICH NORMAN A. BENDER I BY MAGNETIZING APPARATUS AND METHODBACKGROUND OF THE INVENTION unmagnetized bars of permanent magnetmaterial are secured to the shaft and the outer periphery of the bars isthen machined to receive the laminated ring. The laminated ring havingthe squirrel cage winding previously die-cast therein is thenheat-shrunk onto the bars which, when magnetized, will become thepermanent magnets. Since no keeper is provided for the magnets in theabsence of the laminated ring, and further by reason of the machiningand heat-shrinking operations, it is desirable to magnetize the magnetsfollowing assembly of the rotor member.

Heretofore, such permanent magnet-excited rotor members have beenmagnetized with apparatus employing a pole piece having magnetizingwindings positioned on solid, salient pole pieces, the magnetizingwindings being energized by a capacitor-discharge type power supply withthe capacitors being charged by relatively low DC. voltage provided by amotorgenerator set. With such prior magnetizing apparatus, a period onthe order of l to 1% hours was required for magnetizing six rotors, itthen being necessary to shut down the apparatus for four hours to permitthe windings on the pole pieces to cool.

It is accordingly an object of the invention to provide improvedapparatus and methods for magnetizing a permanent magnet rotor memberfor a dynamoelectric machine.

Another object of the invention is to provide improved apparatus andmethods for magnetizing a permanent magnet rotor member for adynamoelectric machine wherein a substantially greater number of rotormembers may be magnetized in substantially less time than has beenpossible with apparatus heretofore employed.

SUMMARY OF THE INVENTION In the practice of the invention in one form,we provide a stator assembly having the windings distributed in slots ina stator core. In addition, we energize the windings with a power supplyto produce a momentary high voltage pulse thereby to cause a highlypeaked surge of current flow in the windings, l rotor assemblies can bemagnetized in approximately minutes before it is necessary to shut downthe apparatus to permit cooling the windings.

In one preferred exemplification, we provide apparatus for magnetizingmagnetic means comprising one or more magnet members of a rotor deviceor means for a dynamoelectric machine, at least one of the members beingformed of permanently magnetizable material and having at least one pairof areas to be oppositely polarized. The apparatus comprises a laminatedstator core member having a yoke portion with the plurality radiallyinwardly extending teeth defining winding slots therebetween, the teethhaving inner ends defining a bore for receiving the rotor member. Atleast one pair of windings is provided, each comprising a plurality ofconcentric coils distributed in respective ones of the slots, the pairof windings being connected and arranged when energized to form oppositemagnetic poles in the core member respectively aligned with the areas tobe polarized. Power supply means is provided coupled to the windings forproducing thereacross a momentary high voltage pulse of preselectedmagnitude thereby to cause a highly peaked surge of current flow in thewindings.

The subject matter which we regard as our invention is set forth in theappended claims. The invention itself, however, along with furtherobjects and advantages thereof will be best understood by reference tothe following description of a preferred exemplification of theinvention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS HO. 1 is a side elevational view ofthe apparatus embodying the invention that may be used to practice theinvention;

FIG. 2 is a transverse cross-sectional view taken generally along theline 22 of FIG. 1;

FIG. 3 is a side cross-sectional view taken generally along the line 3-3of FIG. 2;

FIG. 4 is an end view as viewed along the line 4-4 of FIG. 3; and

FIG. 5 is a schematic illustration showing a circuit for energizing theapparatus of FIG. 2 and showing one preferred power supply inrudimentary form.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1 of thedrawings, one form of magnetizing apparatus embodying the invention,generally indicated at 10, may be supported on worktable 12 havingprotective enclosure 14 pivotally mounted thereon. Direct current surgepower supply 16 may be of the type disclosed, inter alia, in US. Pat.No. 3,333,329 to C. E. Linkous (assigned to the assignee of the presentapplication) and is energized by source 18 of single phase, alternatingcurrent potential. The power supply 16 is coupled by leads 20 tomagnetizing apparatus 10 for energizing the windings thereof, as willhereinafter be described. Interlock 22 on table 12 is coupled to powersupply 16 for disabling the same when protective enclosure 14 is raisedto permit loading a rotor member to be magnetized into magnetizingapparatus 10, and subsequently to permit removal of the magnetized rotormember.

Referring now additionally to FIGS. 2, 3 and 4, apparatus 10 comprisesstator assembly 24, clamping assembly 26, and a pair of end cap members28,30. Stator assembly 24 comprises stator core member 32 formed of astacked plurality of relatively thin laminations of magnetic materialand having a yoke portion 34 with a plurality of teeth 36 extendingradially inwardly therefrom which define Winding slots 38 therebetween.Teeth 36 have inner ends 40 defining a bore for receiving rotor member42 to be magnetized.

In the illustrated embodiment adapted to magnetize rotor member 42having four magnets 46, teeth 36 are arranged in four circumferentiallyspaced pole groups 47 thereby to define, in conjunction with the coilsof the windings disposed in slots 38 as will hereinafter be described,four poles of alternate magnetic polarity, as indicated in FIG. 2. In aspecific embodiment, a 36 tooth stator core member is employed with twoteeth removed in each quadrant, thereby providing four pole groups 47each having seven teeth 36 defining six winding slots 38 therebetween,adjacent groups of teeth 36 being spaced apart by wider slots 48.

Stator core member 32 is surrounded and embraced by steel ring 50, ring50 being welded to stator core member 32 as at 52 (FIG. 3). Ring 50 andyoke portion 34 of stator core member 32 are longitudinally slit todefine narrow slot 54 communicating with one ofthe wide slots 48 (FIG.2).

Bars 46 of permanently magnetizable material, such as AL- NICO alloymaterial of General Electric Company, are machinedto receive a rotorbody 60 formed of a stack of relatively thin, magnetic materiallaminations. The rotor body 60 also has a squirrel cage winding cast inslots therein (not shown). This squirrel cape winding also includesshort circuiting end rings 62 having fan blades 64 integrally formedthereon. Bars 46 are to be transversely magnetized to form oppositelypolarized regions adjacent their side edges, as best seen in FIG. 2.

Clamping apparatus or assembly 26 is employed to move the facingportions of core member 32 and ring 50 which define slot 54 toward eachother thereby to cause inner ends 40 of teeth 36 to engage and clamp theouter peripheral surface 66 of the rotor body 60 during the magnetizingoperation. Clamping assembly 26 comprises a pair of angle members 68secured to the outer peripheral surface of rotor body 60, as by weldingat 70, respectively adjacent and on either side of slot 54, and a pairof manually actuable lever clamps 72 attached to angle members 68 bystuds 71 and nuts 73. Lever clamps 72 are pivotally mounted on one ofthe angle members 68 and are arranged, when manually pivoted downwardlyas viewed in FIG. 2, to cam the angle members 68 toward each otherthereby to compress ring or split sleeve 50 and core member 32 so as toclamp rotor member 42.

. Referring additionally to FIG. 5, winding means are accommodated bythe pole groups 47. These windings each comprise I one or more groups ofcoils, each group including one or more coil turns. In the preferredembodiment, four field windings 74-1, 74-2, 74-3 and 74-4 are providedeach comprising four serially connected coils 75, 76, 77 and 78. Coils75-78 of each winding-74 are concentrically positioned in distributedfashion in slots 38 of each pole group of teeth, it being observed thatthe largest coil 78 which spans the entire pole group 47 of teetharepositioned in the wider slots 48 (FIG. 2). Each coil 75-78 has sideportions 80 positioned in a respective pair of slots 38 or 48 and endturn portions 82 respectively extending on opposite sides of core member32 (FIG. 3).

Windings 74 are connected in parallel by leads 84, 86 (FIG. and arearranged so'that, when energized, the pole groups 47 of teeth 36 arealternately polarized north and south, and a predetermined magneticfield is established having polarized regions in general alignment withthe predetermined regions of blocks 46 to be magnetized, therebyproducing magnetizing flux therein as shown in the dashed lines 79 inFIG. 2.

End cap members 28, 30 respectively have a rectangular outline (FIG. 4)to permit apparatus to be supported on flat surface 88 of table 12. Endcap members 28, are formed of hardened insulating material, such as ahardened polyester resin reinforced or filled with a fibrous material,such as laminated cloth or paper. End cap members 28, 30 each haveflange portion 90 having an edge 92 abutting the sides of core member 32and ring 50, and an end wall 94, flange portions 90 and end walls 94respectively defining annular cavities 96 which respectively receive andaccommodate end turn portions 82 of coils 75-78. End walls 94respectively have central openings 98 therein aligned with and formingextensions of the bore defined by inner ends of teeth 36. End walls 94respectively have four openings 100 formed therethrough which arerespectively aligned with wide slots 48 of stator core member 32.

Windings 74 are embedded in a mass 95 of relatively soft pottingcompound which fills the unoccupied portions of slots 38 and 48 andcavities 96, and openings 100 in end walls 94 of end cap members 28, 30,as at 102. A mandrel or plug (not shown) is inserted through the fillsopenings 98 and the bore of stator core member 32 during injection ofthe potting compound through openings 100 in one end of cap members 28,30 thus forming a continuous bore 104 with openings 98 formingextensions thereof.

Openings 100 have a slight outward taper (as shown in FIG. 3) and thus,when the potting compound has been injected through openings 100 in oneend cap member 28, 30, slugs 102 which fill openings 100 serve to secureend cap members 28, 30 to stator core member 32 and ring 50. The pottingcompound will flow into and at least partially fill slot 54 in statorcore member 32 and ring (FIG. 2). The potting compound is sufficientlyflexible to accommodate clamping of core member 32 and ring 50 by leverclamps 72. While a number of potting compounds are suitable, we haveemployed a room temperature curing urethane potting compound sold byDevon Co. and identified by that company as Flexane No. 95.

It will be observed that end cap members 28, 30 protect end turns 82 ofcoils -78, and that openings 98 and bore 104 formed in the pottingcompound surrounding end turns 82 form a passageway for guiding rotormember 42 into the bore of stator core member 32. End cap member 30 hasopenings 106 in one side wall communicating with cavity 96 through whichpower supply leads 20 extend.

The parallel connected windings 74 have very low resistance which islower than the resistance of the field windings of prior magnetizingapparatus. In a specific embodiment employing a 28 (out of 36) toothstator core member 32 having a bore diameter of 3.68 inch, coils 75-78of each of the windings 74 were formed of 0.048 inch diameter copperwire and had 15, 30, 35 and 40 turns, respectively, the total resistanceof the parallel-connected windings 74 being 0.189 ohm: 5 percent.

Referring now particularly to FIG. 5, power supply 16 is preferably ofthe type shown in FIG. 15 of the aforesaid Linkous U.S. Pat. No.3,333,329 and further described in detail in that patent. The powersupply 16 is here shown in somewhat simplified form in FIG. 5 hereof forillustrative purposes only. Power supply 16 includes energy storagemeans and is shown here as comprising transformer 108 having full waverectifier 110 coupled across its high voltage secondary winding 112, andcapacitive energy storage means in the form of capacitor bank 114. Thecapacitor bank 114 is coupled to rectifier I10 and secondary winding 112and is charged by the rectified high voltage. Primary winding 116 oftransformer 108 is shown as including a selectively adjustable tap 118thereby selectively to vary the voltage induced in secondary winding112. The portion of primary winding 116 selected by tap 118 is coupledacross source 18 by contacts 120, 122 of control relay 124 and interlockcontacts 22.

Capacitor bank 114 is coupled across leads 20 for discharging throughwindings 74 by contacts 126 of time delay relay 128. Momentary contactstart" push button switch initially connects time delay relay 128 forenergization across source 18 and also initially couples operating coil134 of control relay 124 for energization through normally closedcontacts 132 of time delay relay 128. Energization of operating coil 134of control relay 124 due to momentary closing of switch 130 closessealing contacts 136, thereby maintaining operating coil I34 and timedelay relay 128 energized despite opening of switch 130, energization ofoperating coil 134 closing line contacts 120, 122 to energizetransformer 108 thereby to initiate charging of capacitor bank 114. In aspecific embodiment, capacitor bank 114 is charged to 4,200 volts D.C.Upon expiration of the time delay period of time delay relay 128, 15seconds in the specific embodiment, time delay relay 128 closes contacts126 and simultaneously opens contacts 132. Capacitor bank 114 is thuscoupled across leads 20 and the parallel-connected windings 74 thusdischarging through the windings, opening of contacts 132 resulting inde-energization of operating coil 134 thus opening its contacts 120, 122and 136 to de-energize transformer 108 and operating coil 134, and alsode-energizing time delay relay 128. Discharge of capacitor bank 114produces across the parallel-connected windings 74 a momentary highvoltage pulse thereby causing a highly peaked surge of current flow inthe windings. This in turn results in establishing a highly peakedmagnetic field, as will be understood. In practice, power supply 18 isactuated twice in rapid succession for magnetizing each rotor assembly42 in order to insure complete magnetization of magnets 42.

The exemplified distributed winding arrangement provides more iron forthe generated magnetic flux. Further, we have varying from l% inches to3 inches, and four magnets 42, used in synchronous motors from 1/12 to lhorsepower (at 60 cycles), it has been found that rotor assemblies canbe magnetized in minutes before it becomes necessary to shut down theapparatus for cooling the windings, whereas in the prior magnetizingapparatus only six rotor assemblies could be magnetized in a period oftime varying from 1 to 1% hours, shutting down of the apparatus thenbeing necessary for cooling purposes.

While a preferred form of apparatus and one preferred method has beenillustrated and described in connection with magnetizing a particularrotor assembly incorporating four magnets, it will be readily apparentthat the apparatus and method may be employed for magnetizing othertypes of permanent magnet rotor assemblies comprising difierent magnetconfigurations and/or a lesser or greater number of magnets.

While in accordance with the Patent Statutes, we have described what atpresent are considered to be preferred exemplifications of theinvention, it will be obvious to those skilled in the art that numerouschanges and modifications may be made therein without departing from thetrue spirit and scope of the invention, and it is therefore aimed in thefollowing claims to cover all such modifications.

What we claim. as new and desire to secure by Letters Patent of theUnited States ls:

1. Apparatus for magnetizing magnetic means for a rotor device for adynamoelectric machine, the magnetic means including at least one memberformed of permanently magnetizable material and having at least one pairof predetermined regions to be oppositely polarized, said apparatuscomprising a magnetic stator core member having a yoke portion with aplurality of radially inwardly extending teeth defining winding slotstherebetween, said teeth having inner ends defining a bore for receivingsaid rotor member, at least one pair of windings each comprising coilturns accommodated in selected ones of said slots, said pair of windingsbeing connected and arranged when energized to establish a predeterminedmagnetic field and thereby magnetize the at least one member and formopposite magnetic poles in the member along the predetermined regionsthereof, and power supply means coupled to said windings for producingthereacross a momentary high voltage pulse of preselected magnitudethereby to cause a highly peaked surge of current flow in said windings.

2. The apparatus of claim 1 wherein each of the pair of windingscomprise a plurality of distributed coil turns.

3. The apparatus of claim 2 wherein the at least one pair of windingsare connected in parallel.

4. The apparatus of claim I wherein the power supply means includesenergy storage means, and includes means for sequentially coupling theenergy storage means across a high voltage source thereby to storeenergy therein, and thereafter across said windings thereby to producesaid pulse.

5. The apparatus of claim 4 wherein said coupling means includes timedelay means for initially coupling said energy storage means across thehigh voltage source for a predetermined time interval and thereaftercoupling said energy storage means with the windings.

6. The apparatus of claim 1 wherein the stator core member includes ateast one pair of circumferentially spaced pole groups of teeth, eachspaced pole group of teeth defining the slots in which the coilscomprising a winding associated therewith are accommodated, and eachforming a magnetic pole when the respective winding associated therewithis ener-,

gized.

insulating material substantially filling the gap.

9. The apparatus of claim 7 wherein the windings each comprise coilshaving side turn portions respectively positioned in selected ones ofthe slots and end turn portions respectively extending from oppositesides of said core member, the apparatus further comprising a pair. ofend cap members respectively abutting said opposite sides of said coremember and respectively having cavities therein for accommodating saidend turn portions, at least one of said end cap members having anopening therethrough forming an extension of said bore, and means forsecuring said end cap members and core member in assembled relation.

10. The apparatus of claim 9 wherein said windings are embedded in amass of relatively flexible insulating material, said insulatingmaterial substantially fills the gap and the end cap member cavities,and said securing means comprises opening defining surfaces in said endcap members which are substantially filled with said insulatingmaterial.

11. The apparatus of claim 10 further comprising a metallic ringembracing said core member, said ring having a slit in general alignmentwith the core member gap, said end cap members respectively abutting theopposite sides of said ring, and said moving means comprising clampingmeans for deforming said ring.

12. The apparatus of claim 11 wherein there are at least one pair ofspaced pole groups of said teeth, each said pole group of teeth definingthe preselected slots in which the coils comprising one winding aredistributed and forming a magnetic pole when the respective winding isenergized, said windings being connected in parallel and havingrelatively low resistance, the power supply means being of the capacitordischarge type and including time delay means for initially coupling acapacitor across a high voltage direct current potential for apredetermined relatively short charging interval and thereafter couplingsaid capacitor across said windings thereby to produce the pulse.

13. A method of magnetizing at least two spaced apart predeterminedregions of at least two magnetizable members for a dynamoelectricmachine rotor device, the method comprising the steps of: positioningthe rotor device within a bore formed by a stator core assembly havingwindings accommodated in slots formed by teeth thereof and aligningpreselected regions of the magnetizable members relative to the statorcore assembly; clamping the stator core against the rotor device tomaintain the alignment of the rotor device and stator core assembly;establishing a highly peaked magnetic field in the preselected regionsof the magnetic core by surging a highly peaked voltage through thewindings thereby to magnetize the magnetizable members, and removing therotor device from the stator core assembly.

14. The method of claim 13 wherein the step of establishing a highlypeaked magnetic field includes charging energy storage means for a highpotential direct current source during a relatively short charginginterval, and rapidly discharging the energy storage means through thewindings on the stator core assembly.

1. Apparatus for magnetizing magnetic means for a rotor device for adynamoelectric machine, the magnetic means including at least one memberformed of permanently magnetizable material aNd having at least one pairof predetermined regions to be oppositely polarized, said apparatuscomprising a magnetic stator core member having a yoke portion with aplurality of radially inwardly extending teeth defining winding slotstherebetween, said teeth having inner ends defining a bore for receivingsaid rotor member, at least one pair of windings each comprising coilturns accommodated in selected ones of said slots, said pair of windingsbeing connected and arranged when energized to establish a predeterminedmagnetic field and thereby magnetize the at least one member and formopposite magnetic poles in the member along the predetermined regionsthereof, and power supply means coupled to said windings for producingthereacross a momentary high voltage pulse of preselected magnitudethereby to cause a highly peaked surge of current flow in said windings.2. The apparatus of claim 1 wherein each of the pair of windingscomprise a plurality of distributed coil turns.
 3. The apparatus ofclaim 2 wherein the at least one pair of windings are connected inparallel.
 4. The apparatus of claim 1 wherein the power supply meansincludes energy storage means, and includes means for sequentiallycoupling the energy storage means across a high voltage source therebyto store energy therein, and thereafter across said windings thereby toproduce said pulse.
 5. The apparatus of claim 4 wherein said couplingmeans includes time delay means for initially coupling said energystorage means across the high voltage source for a predetermined timeinterval and thereafter coupling said energy storage means with thewindings.
 6. The apparatus of claim 1 wherein the stator core memberincludes at east one pair of circumferentially spaced pole groups ofteeth, each spaced pole group of teeth defining the slots in which thecoils comprising a winding associated therewith are accommodated, andeach forming a magnetic pole when the respective winding associatedtherewith is energized.
 7. The apparatus of claim 1 wherein said yokeportion is longitudinally slit thereby forming facing portions whichnormally define a relatively narrow gap therebetween, and furthercomprising means for moving said facing portions toward each otherthereby causing the inner ends of the teeth to engage and clamp a rotordevice positioned adjacent thereto.
 8. The apparatus of claim 7 whereinthe windings are embedded in a mass of relatively flexible insulatingmaterial, the insulating material substantially filling the gap.
 9. Theapparatus of claim 7 wherein the windings each comprise coils havingside turn portions respectively positioned in selected ones of the slotsand end turn portions respectively extending from opposite sides of saidcore member, the apparatus further comprising a pair of end cap membersrespectively abutting said opposite sides of said core member andrespectively having cavities therein for accommodating said end turnportions, at least one of said end cap members having an openingtherethrough forming an extension of said bore, and means for securingsaid end cap members and core member in assembled relation.
 10. Theapparatus of claim 9 wherein said windings are embedded in a mass ofrelatively flexible insulating material, said insulating materialsubstantially fills the gap and the end cap member cavities, and saidsecuring means comprises opening defining surfaces in said end capmembers which are substantially filled with said insulating material.11. The apparatus of claim 10 further comprising a metallic ringembracing said core member, said ring having a slit in general alignmentwith the core member gap, said end cap members respectively abutting theopposite sides of said ring, and said moving means comprising clampingmeans for deforming said ring.
 12. The apparatus of claim 11 whereinthere are at least one pair of spaced pole groups of said teeth, eachsaid pole group of teeth defining the preselected slots in which thecoils comprising one winding Are distributed and forming a magnetic polewhen the respective winding is energized, said windings being connectedin parallel and having relatively low resistance, the power supply meansbeing of the capacitor discharge type and including time delay means forinitially coupling a capacitor across a high voltage direct currentpotential for a predetermined relatively short charging interval andthereafter coupling said capacitor across said windings thereby toproduce the pulse.
 13. A method of magnetizing at least two spaced apartpredetermined regions of at least two magnetizable members for adynamoelectric machine rotor device, the method comprising the steps of:positioning the rotor device within a bore formed by a stator coreassembly having windings accommodated in slots formed by teeth thereofand aligning preselected regions of the magnetizable members relative tothe stator core assembly; clamping the stator core against the rotordevice to maintain the alignment of the rotor device and stator coreassembly; establishing a highly peaked magnetic field in the preselectedregions of the magnetic core by surging a highly peaked voltage throughthe windings thereby to magnetize the magnetizable members, and removingthe rotor device from the stator core assembly.
 14. The method of claim13 wherein the step of establishing a highly peaked magnetic fieldincludes charging energy storage means for a high potential directcurrent source during a relatively short charging interval, and rapidlydischarging the energy storage means through the windings on the statorcore assembly.